My 66 amazon has rust in some places I can't get into with a tool. This started with a fuel tank replacement, and has blossomed into a rust-hunt all around the inside of the trunk. Finding plenty, much more than I expected. Some places are obvious, like the quarter-size patches that came to light when I peeled up the stuck-on oem matting. These I gouge severely with a wire wheel on a battery drill. But I've started to notice that whenever I chip up some caulking (gray in color, and painted with oem paint) there's usually more rust. Some of the puttied places are tight narrow spaces, like between the back of the wheel well and the side wall. I have been using POR stuff on the engine and other parts. Can I just pour a dose of Metal Ready (POR phosphoric acid) down these crevices, followed by time to dry and then some POR paint? Going back outside now, chip, chip, chip.